Oxide-zone tellurium minerals are relatively rare worldwide, but often occur as attractive microcrystals that are highly sought after by micromounters. Table 1 is a list of the 71 known Te-oxide minerals, 68 of which are considered valid species; most are either tellurite (Te4+O3)2- or tellurate (Te6+O6)6- species. Also included are information on the type locality, the year that each mineral was described in the literature, and whether the mineral is considered a valid species (Y = yes, Q = questionable).
Remarkably, over 60% of the species (43 out of 71) were discovered at only four deposits: Moctezuma, Mexico; Tombstone, Arizona; Centennial Eureka Mine, Utah; and Otto Mountain, California. In fact, nearly a third of all Te-O mineral species were discovered in just one deposit: Moctezuma. Many of these species are still found at only one locality today.
The chemistry of the Te-oxide minerals naturally reflects the types of deposits in which they are found. The four leading occurrences listed above are all oxidized base metal deposits, and not surprisingly, 60% of all Te-O minerals contain Pb and/or Cu. If Zn and Fe are added in, this increases to 84%. Although primary Te minerals are often associated with gold and silver deposits, these elements are almost never essential chemical constituents in the oxidized Te minerals (with one exception – quetzalcoatlite contains a small amount of silver). However, gold and silver minerals are often found in close association with the Te-O minerals.
Prior to 1960, only seven Te-oxide minerals were known – two of which are now considered to be questionable species. In the 1960s and 1970s, there was a rapid expansion in the number of new Te-O species (28 new species in 20 years) which coincided with mineralogical studies of the Moctezuma and Tombstone deposits. Another 24 species were added in the 1980s and 1990s, but these represent a somewhat wider range of occurrences. The most notable new find during this period was the discovery of six new species from the Centennial Eureka Mine, Tintic District, Utah. One of these new species (eurekadumpite) was just described in 2010. Only four new species were described between 2000 and 2009, but in 2010 a new occurrence at Otto Mountain, California was described by Tony Kampf and his colleagues that has produced seven new species (see American Mineralogist, v. 95) with more likely to come.
Although there are presently a small number of worldwide occurrences for Te-O mineral species, the rather unique geochemistry of these deposits appears to favor the formation of new mineral species. It therefore seems likely that as more tellurium-bearing deposits are investigated, there will be a corresponding increase in the number of Te-oxide mineral species.